As diseases associated with the activity of vanilloid receptor, pain, acute pain, chronic pain, neuropathic pain, post-operative pain, migraine, arthralgia, neuropathies, nerve injury, diabetic neuropathy, neurodegeneration, neurotic skin disorder, stroke, urinary bladder hypersensitiveness, irritable bowel syndrome, a respiratory disorder such as asthma or chronic obstructive pulmonary disease, irritation of skin, eye or mucous membrane, fervescence, stomach-duodenal ulcer, inflammatory bowel disease and inflammatory diseases can be enumerated. The present invention provides pharmaceutical compositions for prevention or treatment of these diseases.
Yet, the diseases described above are only for enumeration, not to limit the scope of clinical application of vanilloid receptor antagonist.
Capsaicin (8-methyl-N-vanillyl-6-nonenamide) is a main pungent component in hot peppers. Hot peppers have been used, for a long time, not only as a spice but also as traditional medicine in the treatment of gastric disorders and when applied locally, for the relief of pain and inflammation (Szallasi and Blumberg, 1999, Pharm, Rev. 51, pp159–211). Capsaicin has a wide spectrum of biological actions, and not only exhibits effects on the cardiovascular and respiratory systems but also induces pain and irritancy on local application. Capsaicin, however, after such induction of pain, induces desensitization, both to capsaicin itself and also to other noxious stimuli to make the pain stopped. Based on this property, capsaicin and its analogues such as olvanil, nuvanil, DA-5018, SDZ-249482, resiniferatoxin are either used as analgesic agent, therapeutic agent for incontinentia urinae or skin disorder, or under development (Wriggleworth and Walpole, 1998, Drugs of the Future 23, pp 531–538).
Transmissions of mechanical, thermal and chemical noxious stimuli are mainly occurred by primary afferent nerve fibers of fine unmyelinated nerve (C-fiber) and thin myelinated nerve (A-fiber), and main reaction site of capsaicin and its analog called vanilloid is present at the nerve fiber transmitting the noxious stimuli. Capsaicin acts at the receptor existing on these neurons to induce potent stimuli by causing potent inflow of mono-and di-valent cations such as calcium and sodium, then exhibits potent analgesic effect by blocking the nervous function (Wood et al., 1988, J. Neurosci, 8, pp3208–3220). Vanilloid receptor (VR-1) has been recently cloned and its existence becomes clear(Caterina et al., 1997, Nature 389, pp816–824). It was clarified that this receptor transmits not only stimuli by capsaicin anlogues(vanilloid) but also various noxious stimuli such as proton and thermal stimuli (Tominaga et al., 1998, Neuron 21, pp531–543). Based on this, it is considered that vanilloid receptor functions as a integrative modulator against various noxious stimuli and carries out critical role in transmissions of pain and noxious stimuli. Recently, knock-out mouse in which gene encoding for vanilloid receptor was deleted was prepared (Caterina et al., 2000, Science 288, pp306–313; Davis et al., 2000, Nature 405, pp183–187). Compared to normal mice, the mouse was found out to exhibit much reduced reaction to thermal stimuli and thermal pain, while exhibiting no difference in general behavior, reconfirming the importance of the receptor in transmission of noxious signal. However, except proton, no other endogenous ligand, not exogenous ligand such as capsaicin, actually involved in transmission of noxious stimuli at vanilloid receptor was known. It is considered that leucotriene metabolite represented by 12-hydroperoxyeicosatetraenoic acid (12-HPETE) (Hwang et al., 2000, PNAS 11, pp6155–6160) and arachidonic aicd derivatives such as anandamide (Zygmunt et al., 2000, Trends Pharmocol. Sci. 21, pp43–44) act as the most likely endogenous ligand for the receptor and proton acts as a cofactor with receptor-stimulating activity, rather than as a direct ligand.
As such, a capsaicin-sensitive sensory nerve cell and a vanilloid receptor existing in the cell are distributed over the entire body and play basic function in transmission of noxious stimuli and pain, further act as crucial factor in expression of neurogenic inflammation, thereby to have close relation with the cause of neuropathies, nerve injury, stroke, asthma, chronic obstructive pulmonary diseases, urinary bladder hypersensitiveness, irritable bowel syndrome, inflammatory bowel disease, fervescence, skin disorder and inflammatory disease. Lately, their correlation even with neuropathic disease is suggested (WO 99/00125). Recently, attention has focused to the role of afferent sensory nerve responding to capsaicin in gastrointestinal injury, and it was proposed that the afferent nerve might have a dual character that it exhibits protective action against gastric damage by improving gastric microcirculation through releasing peripheral neuropeptide such as CGRP (calcitonin gene-related peptide), while inducing gastric injury by stimulating sympathetic nervous system (Ren et al., 2000, Dig. Dis. Sci. 45, pp830–836). It is determined that vanilloid receptor antagonist has very high potential to be used for prevention or treatment of the said various diseases by blocking the vanilloid receptor conducting such varied functions.
Though it may be, theoretically, anticipated that antagonist for this receptor would exhibit substantial degree of inhibitory action against pain and neurogenic inflammation, it was found out that the competitive antagonist for this receptor, capsazepine, almost the only one known until now, failed to exhibit significant analgesic and anti-inflammatory effects (Perkins and Campbell, 1992, Br. J. Pharmacol. 107, pp329–333). Therefore, not much progress was made on this field. However, recently, there has been a report on significant results for analgesic action of capsazepine in animal studies (Kwak et al., 1998, Neurosci. 86, pp619–626; Santos and calixto, 1997, Neurosci. Lett. 235, pp73–76), in particular, the inventors of the present invention clearly demonstrated through animal studies the analgesic and anti-inflammatory effects of the strong vanilloid receptor antagonists which were identified through experiments in laboratory, and based on this, strongly suggested the development potential of vanilloid receptor antagonist as an analgesic and anti-inflammatory agent. Yet, though the vanilloid receptor antagonist derived from the present studies will mainly act based on the antagonistic activity of itself, even a possibility that it could exhibit the pharmacological activity through transformation into agonist via metabolism after absorption into body is not to be excluded.
To resolve the problems described above, the present invention is to provide novel compounds which are selectively antagonistic to vanilloid receptor and exhibit analgesic and anti-inflammatory effects while causing no irritancy, and pharmaceutical compositions containing the same.